In some trials performance was assessed by carrying out tasks such as driving. Others subjected volunteers to neuropsychological tests.

Caffeine appeared to reduce errors more than 'dummy' placebo treatments or naps, according to the results published in the Cochrane Database of Systematic Reviews.

It also improved performance in various tests, including those of memory, attention, perception, conceptualising and reasoning.

Lead researcher Dr Katherine Ker, from the London School of Tropical Medicine, said: 'It seems reasonable to assume that reduced errors are associated with fewer injuries, although we cannot quantify such as reduction.'

The average age of people taking part in the trials was between 20 and 30.

Because the effects of body clock disruption vary with age, more research is needed to see if caffeine improved the alertness of older workers, said the scientists.